1. Field of the Invention
The present invention relates to an angular velocity sensor for detecting an angular velocity about at least an axis. Particularly, the present invention relates to a biaxial angular velocity sensor of an oscillation-type for detecting angular velocities about two axes.
2. Related Background Art
Conventionally, there is a proposal of an oscillation-type angular velocity sensor in which the angular velocity of an object is acquired by detecting Coriolis' force appearing in response to input of an angular velocity into a mass portion performing a reference oscillation. As the sensor of this type, there have been proposed some oscillation-type angular velocity sensors fabricated on semiconductor substrates using techniques of MEMS (Micro-Electro Mechanical Systems).
In general, in the oscillation-type angular velocity sensor using a semiconductor substrate, an angular velocity is obtained by measuring a displacement of a detecting mass portion caused by Coriolis' force appearing in response to input of the angular velocity about an axis perpendicular to the mass portion performing a reference oscillation.
Further, there is a demand in the fields of home appliances, robots and the like for detection of angular velocities about plural axes for controlling motions or operations. To satisfy such demand, angular velocity sensors capable of detecting angular velocities about two axes have been proposed (see JP 1995-120266 A and JP 1997-127148 A). JP 1995-120266 A discloses an oscillation-type angular velocity sensor in which two uni-axial angular velocity sensor structures are disposed on a semiconductor substrate, being shifted from each other by an angular placement of 90 degrees, so that angular velocities about two axes can be measured.
FIGS. 11A and 11B illustrate a schematic structure of the biaxial angular velocity sensor disclosed in JP 1995-120266 A. This sensor includes two oscillators (mass portions) 601 and 602, and two driving portions 603 and 604 that respectively supply driving forces 657 and 658 to the oscillators 601 and 602 to excite reference oscillations 651 and 652 of these oscillators. While Coriolis' forces 653 and 654 are generated in a direction of the same axis, angular velocities 655 and 656 are detected using two systems of detecting electrodes, respectively.
Further, JP 1997-127148 A discloses an oscillation-type angular velocity sensor in which Coriolis' forces in different directions occur in an oscillator in response to angular velocities about two axes, and angular velocities about two axes are obtained by measuring displacements of the oscillator in the directions of Coriolis' forces, respectively.
FIGS. 11C and 11D illustrate the biaxial angular velocity sensor disclosed in JP 1997-127148 A. In each detecting system for detecting each angular velocity about an axis, a driving portion 607 or 608 supplies driving force 677 or 678 to an oscillator (mass portion) 605 or 606 to cause a reference oscillation 671 or 672 of the oscillator 605 or 606. Here, Coriolis' forces 673 and 674 in different directions occur in response to input of angular velocities 675 and 676 about axes, and the oscillator 605 or 606 is displaced in a direction corresponding Coriolis' force 673 or 674. These displacements are measured using two systems including detecting electrodes, respectively.
In the above biaxial angular velocity sensor using the semiconductor substrate, however, a system of a pair of detecting electrodes and a displacement detecting circuit is necessary for each angular velocity detecting axis. Accordingly, a system for performing multi-axis detection needs to include plural pairs of detecting electrodes and plural displacement detecting circuits. Hence, the construction of the system is liable to be complicated.